The present invention relates to a progressive engagement friction disc, particularly for use as a driven plate in a clutch, comprising a hub and at least two friction linings fixed on both sides of blades disposed in a circular series and fastened to at least one annular washer coupled to the hub, each blade having plane areas distributed in at least two sets which adjoin the two respective friction linings, the latter being fixed thereto, and which extend at slightly different levels in two parallel planes, and ramp means connecting the plane areas of one of the sets to the plate areas of the other set.
The blades may be composed of small individual parts which are easy to manufacture without loss of material, and are fixed to the washer by any suitable means. However, they may also all form together an integral annular whole, which is either separate from the washer and attached thereto by any suitable means or is itself integral with this washer.
The washer is generally coupled to the hub either by direct fastening, or with the aid of a device permitting limited torsion under the control of resilient means, with a frictional damping effect.
The plane areas of the blades are situated in parallel planes on at least two slightly different levels and, through the resilient axial compression of the blades, permit progressive engagement when the disc is gripped at its friction linings inside the clutch.
It will be appreciated that during this axial compression of the disc, the areas of one of the levels, which will be called fixed areas, are allowed to retain the same axial position relative to the washer, and the areas of the other level, which will be called movable areas, are allowed to move axially closer to the fixed areas in the course of the flattening of the blade.
The use of compressible blades is advantageous for obtaining a progressive action not only at the time when engagement is effected, in order to avoid jerkiness, but is also useful while the clutch remains in the engaged state, because it makes it possible to compensate for manufacturing and assembly tolerances of the various parts of the clutch, as well as for deformation due to heat which may occur in the course of operation.
The ramps connect together the plane areas lying at different levels, thus giving the blade satisfactory strength and at the same time excellent resilient compressibility.
In general, the plane areas, or at least some of them, are narrow in a circumferential direction, so that it is difficult to fasten the linings to them, for example by riveting and/or adhesive bonding. In order to strengthen the riveting, it is of course possible to contemplate increasing the number of rivets by placing more of them on the same radial line, having regard to the circumferential narrowness of the area, but, if this is done, there is danger that a line of reduced strength will be formed in the blade and the linings.
The object of the present invention is a progressive engagement friction disc of the kind described above, particularly for a clutch, in which the conditions of the fastening of the linings to the blades, particularly by rivets, are substantially improved, while at the same time the construction is convenient and strong, and operation is excellent.